While electric drive trains comprise an increasing share of drive trains used in industrial material manipulation and transportation, such drive trains have not yet been able to provide the full simplification and ease of use that it was once thought they would provide. For example, although the speed range of an electric motor may differ from, and in some cases exceed, the speed range of a counterpart internal combustion engine, electric motors do not typically have sufficient speed and torque range to allow continuous operation from machine stop to machine full speed.
As such, electric drive machines generally include a shiftable transmission much like their internal combustion driven counterparts to allow the electric drive motor to operate within its specified speed range while also allowing the machine to have a full range of output/driving speed. Thus, for example, a low speed range may provide operation between a stopped state and some intermediate speed state, while a high speed range, entered at or near the top speed of the low range state, would provide enough speed for increasingly higher speeds, e.g., for extended transport runs.
However, for all the benefits that they provide, multi-range shiftable transmissions also entail certain significant shortcomings. For example, as the transmission is shifted between ranges, inertial problems may occur and must be accounted for in the transmission design and operation. Moreover, in conjunction with low range operation, sufficiently low gearing and sufficiently large inverters must be provided to allow for the required machine stall torque. Overcoming these and other problems can lead to significant costs and complexities, offsetting, at least to some extent, the many benefits of the electric drive system.
It will be appreciated that this background description has been created by the inventors to aid the reader, and is not to be taken as a reference to prior art nor as an indication that any of the indicated problems were themselves appreciated in the art.